Understanding the Triangles: A Practical Roadmap of the Cavernous Sinus

Background: The cavernous sinus (CS) houses important neurovascular structures. Understanding the anatomy of CS is important to properly address pathologies within this region. Objective: This study presents a detailed description of the CS anatomy emphasizing the related surgical approaches and key anatomical triangles and compartments used to access this region during open and expanded endoscopic approach (EEA). Method: Four formalin-fixed, latex-colored anatomical specimens were utilized. Dissections were performed under microscope and endoscope for better visualization. The CS was dissected to highlight its most important features and landmarks to be taken into account in the operating room. Result: The clinoidal (Dolenc) triangle can be accessed via orbitozygomatic approach (OZA) and transorbital approach (TOA). The endoscopic endonasal (EEA) transsphenoidal-transethmoidal approach provides limited access to this triangle located between the ON and CN III. In this triangle, from anterior to posterior, resides the optic strut, clinoidal segment of ICA, and carotid-oculomotor membrane. The oculomotor (Hakuba) triangle is bounded by three ligaments: the interclinoidal ligament medially, the anterior petroclinoid ligament laterally, and the posterior petroclinoid ligament posteriorly. This triangle provides access to the medial and posterior aspect of the CS. Access to this area and its contents is feasible with the OZA, TOA/TONES but limited with an EEA. The supratrochlear triangle is located between the lower border of CN III, upper margin of CN IV, and the line which connects the dural entry points of these two nerves. This triangle can be reached with a pterional or an OZA. Through a TONES, complete exposure to this area is also feasible. With an EEA, exposure of the apex of this triangle where CNs III and IV merge to pass through the SOF is achievable after medialization of the ICA. The infratrochlear (Parkinson) triangle is bounded by the lower margin of CN IV, the upper border of V1, and the line that connects the entry points of CN IV and V1 into the dura and Meckel’s cave respectively. This triangle can be accessed via both OZA and TOA. It is difficult to reach the posterior compartment of this triangle through an EEA and can be performed after mobilization of the cavernous ICA. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany